Here’s a slightly different version of the battle between Luke Skywalker and Darth Vader at the end of Star Wars: The Empire Strikes Back. It’s just one of many revelations in a new making-of book. More rare concept art below.

The Making of Star Wars: The Empire Strikes Back by J.W. Rinzler comes out today, and it’s not just essential for fans of the classic film. It’s also a must-read for anybody who’s interested in the creative process, because it goes into excruciating detail, on a day-to-day basis, on the troubled genesis of an amazing film.

You get inside the heads of everybody involved with it, and you see how much pain went into every frame of this movie. In particular, there’s a 17-page section in which you get a transcript of director Irvin Kershner and the actors — especially Harrison Ford — agonize over every second of the crucial carbonite freezing chamber scene, trying to get as much emotional truth and reality out of it as possible. This was on set, after the screenplay had already been revised several times, and every moment of that sequence gets rehashed and debated until it’s (arguably) perfect. There’s tons and tons of eye-popping concept art, including tons of versions of the Luke/Vader fight.

What Rinzler’s book drives home is that Empire Strikes Back was as groundbreaking and daring, in its own way, as the original Star Wars. The film went way over schedule and massively over budget, and almost ran out of money a bunch of times. Everybody became sick on set, Mark Hamill broke his thumb doing one stunt, and there was an accident with the bacta tank that could have killed Hamill if he’d been inside. Also, the movie’s second unit director and its first screenwriter both died during the process.

You see how George Lucas put together ESB at the same time that he was building his business empire, including Lucasfilm and the more mature version of Industrial Light & Magic. Lucas was creating his team and fighting for creative freedom, even as he was stepping back from writing and directing — and a big part of this movie’s brilliance stems from Lucas’ drive to finance the film himself, keeping 20th Century Fox out of the loop creatively. (And if Empire had failed, Lucas would have been broke, despite the first film’s huge profits.